Lubricant-impregnated bushing for impact tool

ABSTRACT

A power tool includes a housing having a motor housing portion and a front casing coupled to the motor housing portion. The power tool also includes an electric motor positioned within the motor housing portion, a drive assembly having an output shaft to which a tool element for performing work on a workpiece is attachable, and a powdered metal bushing disposed within the front casing that rotatably supports the output shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to co-pending U.S. Provisional PatentApplication No. 62/700,725, filed on Jul. 19, 2018, the entire contentof which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to power tools, and more specifically toimpact tools.

BACKGROUND OF THE INVENTION

Impact tools, such as impact drivers and impact wrenches, are typicallyutilized to provide a striking rotational force, or intermittentapplications of torque, to a tool element or workpiece (e.g., afastener) to either tighten or loosen the fastener.

SUMMARY OF THE INVENTION

The present invention provides, in one aspect, a power tool including ahousing having a motor housing portion and a front casing coupled to themotor housing portion. The power tool also includes an electric motorpositioned within the motor housing portion, a drive assembly having anoutput shaft to which a tool element for performing work on a workpieceis attachable, and a powdered metal bushing disposed within the frontcasing that rotatably supports the output shaft.

The present invention provides, in another aspect, an impact toolincluding a housing having a motor housing portion and a front casingcoupled to the motor housing portion. The impact tool also includes anelectric motor positioned within the motor housing portion and a driveassembly having an anvil, a shaft configured to receive torque from theelectric motor, and a hammer. The hammer is configured to impartconsecutive rotational impacts upon the anvil. The impact tool furtherincludes a lubricant-impregnated bushing disposed within the frontcasing that rotatably supports the anvil.

The present invention provides, in yet another aspect, a method ofmanufacturing a power tool. The method includes forming a bushing frompowdered metal by compacting and sintering the powdered metal. Themethod further includes inserting the bushing into a mold cavity andmolding a gear case of the power tool in the mold cavity around thebushing. The method further includes immersing the gear case inlubricant so that the lubricant is wicked into the bushing to impregnatethe bushing with the lubricant.

Other features and aspects of the invention will become apparent byconsideration of the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an impact tool according to oneembodiment.

FIG. 2 is a cross-sectional view of the impact tool of FIG. 1, takenalong line 2-2 in

FIG. 1.

FIG. 3 is an enlarged cross-sectional view of a portion of the impacttool illustrated in FIG. 2.

FIG. 4 is exemplary flow chart describing one embodiment of the methodfor preparing a powdered metal bushing and front casing for an impacttool.

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting.

DETAILED DESCRIPTION

FIG. 1 illustrates a power tool in the form of a rotary impact tool 10.The impact tool 10 includes a housing 14 with a motor housing portion18, a front housing portion or gear case 22 coupled to the motor housingportion 18 (e.g., by a plurality of fasteners), and a handle portion 26disposed underneath the motor housing portion 18. The handle portion 26includes a grip 27 that can be grasped by a user operating the impacttool 10. In the illustrated embodiment, the handle portion 26 and themotor housing portion 18 are defined by cooperating clamshell halves 29a, 29 b.

With continued reference to FIG. 1, the impact tool 10 has a batterypack 34 removably coupled to a battery receptacle 38 located at a bottomend of the handle portion 26. The battery pack 34 includes a housing 39supporting battery cells 40 (FIG. 2), which are electrically connectedto provide the desired output (e.g., nominal voltage, current capacity,etc.) of the battery pack 34. A battery power display 53 indicates thepower level remaining in the battery pack 34 (FIG. 1). In otherembodiments, the impact tool 10 may include a power cord forelectrically connecting the impact tool 10 to a source of AC power. As afurther alternative, the impact tool 10 may be configured to operateusing a different power source (e.g., a pneumatic power source, etc.).

In the illustrated embodiment, the impact tool 10 includes a light 41(e.g., an LED light) located at the top end of the handle portion 26 andjust below the gear case 22. The light 41 is oriented so as toilluminate a workpiece during operation of the impact tool 10. The light41 preferably draws power from the battery pack 34 and may automaticallyilluminate during operation of the impact wrench 10 and shut off after apredetermined time period following operation of the impact tool 10.

Referring to FIG. 2, an electric motor 42, supported within the motorhousing portion 18, receives power from the battery pack 34 when thebattery pack 34 is coupled to the battery receptacle 38. The motor 42 ispreferably a brushless direct current (“BLDC”) motor having a rotor oroutput shaft 50. A button 52, extending laterally from the housing 14,allows an operator to change the direction that the motor 42 rotates theoutput shaft 50. The output shaft 50 is rotatable about an axis 54. Afan 58 is coupled to the output shaft 50 (e.g., via a splinedconnection) behind the motor 42. The impact tool 10 also includes atrigger 62 coupled to the handle portion 26 that is actuatable toselectively electrically connect the motor 42 and the battery pack 34 toprovide DC power to the motor 42.

With reference to FIG. 3, the impact wrench 10 further includes a gearassembly 66 coupled to the motor output shaft 50 and a drive assembly 70coupled to an output of the gear assembly 66. The gear assembly 66 is atleast partially housed within the gear case 22. The gear assembly 66 maybe configured in any of a number of different ways to provide a speedreduction between the output shaft 50 and an input of the drive assembly70.

The illustrated gear assembly 66 includes a pinion 82 formed on themotor output shaft 50, a plurality of planet gears 86 meshed with thepinion 82, and a ring gear 90 meshed with the planet gears 86 androtationally fixed within the gear case 22. The planet gears 86 aremounted on a camshaft 94 of the drive assembly 70 such that the camshaft94 acts as a planet carrier. Accordingly, rotation of the output shaft50 rotates the planet gears 86, which then orbit along the innercircumference of the ring gear 90 and thereby rotate the camshaft 94.The gear assembly 66 thus provides a gear reduction ratio from theoutput shaft 50 to the camshaft 94. The output shaft 50 is rotatablysupported by a first or forward bearing 98 and a second or rear bearing102.

The drive assembly 70 of the impact tool 10 includes an anvil 200extending from the gear case 22 with a bit holder 202 to which a toolelement (e.g., a screwdriver bit; not shown) can be coupled forperforming work on a workpiece (e.g., a fastener). The drive assembly 70is configured to convert the continuous rotational force or torqueprovided by the motor 42 and gear assembly 66 to a striking rotationalforce or intermittent applications of torque to the anvil 200 when thereaction torque on the anvil 200 (e.g., due to engagement between thetool element and a fastener being worked upon) exceeds a certainthreshold. In the illustrated embodiment of the impact wrench 10, thedrive assembly 66 includes the camshaft 94, a hammer 204 supported onand axially slidable relative to the camshaft 94, and the anvil 200.

The drive assembly 70 further includes a spring 208 biasing the hammer204 toward the front of the impact wrench 10 (i.e., toward the left inFIG. 3). In other words, the spring 208 biases the hammer 204 in anaxial direction toward the anvil 200, along the axis 54. A thrustbearing 212 and a thrust washer 216 are positioned between the spring208 and the hammer 204. The thrust bearing 212 and the thrust washer 216allow for the spring 208 and the camshaft 94 to continue to rotaterelative to the hammer 204 after each impact strike when lugs 218 on thehammer 204 engage with corresponding anvil lugs 220 and rotation of thehammer 204 momentarily stops. A washer may be located between the anvil200 and a front end of the gear case 22 in some embodiments. Thecamshaft 94 further includes cam grooves 224 in which corresponding camballs 228 are received. The cam balls 228 are in driving engagement withthe hammer 204 and movement of the cam balls 228 within the cam grooves224 allows for relative axial movement of the hammer 204 along thecamshaft 94 when the hammer lugs 218 and the anvil lugs 220 are engagedand the camshaft 94 continues to rotate.

With continued reference to FIG. 3, the anvil 200 is rotatably supportedby a bushing 236 fixed within a front portion of the gear case 22. Inthe illustrated embodiment, the bushing 236 is made of powdered metal.The powdered metal construction of the bushing 236 provides the bushing236 with greater porosity than conventional metal bushings. This greaterporosity advantageously allows the bushing 236 to be impregnated with alubricant, such as oil, which provides the bushing 236 withself-lubricating properties. Accordingly, the anvil 200 rotates withless wear and improved stability (i.e. reduced wobble).

FIG. 4 illustrates a method 1000 of manufacturing the bushing 236 andthe gear case 22 of the impact tool 10. First, the bushing 236 is formedat step 1001 via a powdered metal compaction and sintering process.Alternatively, the bushing 236 may be formed from powdered metal usingany other suitable process, such as a laser sintering additivemanufacturing process. Next, at step 1002, the bushing 236 is insertedinto a mold for the gear case 22. The gear case 22 is then molded aroundthe bushing 236 (e.g., in a die casting process), which secures thebushing 236 within the gear case 22 without the need for a subsequentpress-fitting operation or additional fasteners (e.g., snap rings).

Next, at step 1003, the gear case 22 may be machined using a CNC mill ora similar machine tool to achieve desired tolerances and surfacefinishes. The gear case 22 and the bushing 236 may also be cleanedbefore, during or after the machining process, using any of a variety ofmethods, such as ultrasonic cleaning. Ultrasonic cleaning ischaracterized by inducing high frequency sound waves to agitate a liquidor cutting fluid, which is turn exerts strong forces on surfacecontaminants or impurities. Anti-rust or other anti-corrosive additivesmay be added to further increase the effectiveness of the ultrasoniccleaning process.

Next, the gear case 22 (and the bushing 236 contained inside) isimmersed in a liquid lubricant, such as oil, at step 1004. The lubricantis wicked into the pores of the powdered metal bushing 236 by capillaryaction so that the bushing 236 is impregnated with the lubricant. Insome embodiments, after being immersed in the lubricant, the bushing 236has an impregnation ratio (i.e. a ratio of the mass of absorbedlubricant to the mass of the bushing 236) between about 10% and about20%. In some embodiments, the bushing 236 has an impregnation ratio ofabout 15%. The absorbed lubricant may gradually be released from thebushing 236 over time so that the bushing 236 is self-lubricating.Finally, at step 1005, the gear case 22 and/or the powdered metalbushing 236 may be cleaned, painted, or undergo any additional desiredprocessing before further assembly of the impact tool 10 including, forexample, inserting the anvil 200 into the bushing 236.

Referring to FIGS. 1-3, in operation of the impact tool 10, an operatordepresses the trigger 62 to activate the motor 42, which continuouslydrives the gear assembly 66 and the camshaft 94 via the output shaft 50.As the camshaft 94 rotates, the cam balls 228 drive the hammer 204 toco-rotate with the camshaft 94, and the hammer lugs 218 engage,respectively, driven surfaces of the anvil lugs 220 to provide an impactand to rotatably drive the anvil 200 and the tool element. The bushing236 rotatably supports the anvil 200 and gradually releases lubricant tomaintain low-friction operation and to inhibit the anvil 200 fromwobbling.

After each impact, the hammer 204 moves or slides rearward along thecamshaft 94, away from the anvil 200, so that the hammer lugs disengagethe anvil lugs 220. As the hammer 204 moves rearward, the cam balls 228situated in the respective cam grooves 224 in the camshaft 94 moverearward in the cam grooves 224. The spring 208 stores some of therearward energy of the hammer 204 to provide a return mechanism for thehammer 204. After the hammer lugs 218 disengage the respective anvillugs 220, the hammer 204 continues to rotate and moves or slidesforwardly, toward the anvil 200, as the spring 208 releases its storedenergy, until the drive surfaces of the hammer lugs 218 re-engage thedriven surfaces of the anvil lugs 220 to cause another impact.

Although the bushing 236 is shown incorporated in a rotary impact tool10, the bushing 236 may alternatively be used with other rotary powertools (e.g., drills, reciprocating saws, rotary hammers, pulse drivers,etc.) for supporting an output spindle or shaft. In such tools, thebushing 236 substitutes for a roller bearing, such as a needle bearingor a ball bearing, which reduces cost of the tool without reducing thelifespan of the tool.

Various features of the invention are set forth in the following claims.

What is claimed is:
 1. A power tool comprising: a housing including amotor housing portion and a front casing coupled to the motor housingportion; an electric motor positioned within the motor housing portion;a drive assembly including an output shaft to which a tool element forperforming work on a workpiece is attachable; and a powdered metalbushing disposed within the front casing, the bushing rotatablysupporting the output shaft.
 2. The power tool of claim 1, wherein thebushing is impregnated with lubricant such that the bushing isself-lubricating.
 3. The power tool of claim 2, wherein the lubricant isan oil.
 4. The power tool of claim 2, wherein the bushing has animpregnation ratio between about 5% and about 25%
 5. The power tool ofclaim 5, wherein the bushing has an impregnation ratio between about 10%and about 20%.
 6. The power tool of claim 1, wherein the bushing isinsert-molded within the front casing.
 7. The power tool of claim 1,wherein the output shaft is an anvil, and wherein the drive assemblyfurther includes a camshaft configured to receive torque from theelectric motor, a hammer configured to impart consecutive rotationalimpacts upon the anvil, and a gear assembly coupled between the electricmotor and the cam shaft, wherein the gear assembly is at least partiallyhoused within the front casing.
 8. The power tool of claim 7, furthercomprising a bit holder coupled to the anvil, wherein the bit holderprojects from the front casing.
 9. The power tool of claim 1, furthercomprising a handle housing portion extending from the motor housingportion, wherein the handle housing portion includes a batteryreceptacle.
 10. The power tool of claim 1, wherein the bushing is formedby a compaction and sintering process.
 11. An impact tool comprising: ahousing including a motor housing portion and a front casing coupled tothe motor housing portion; an electric motor positioned within the motorhousing portion; a drive assembly including an anvil, a shaft configuredto receive torque from the electric motor, and a hammer configured toimpart consecutive rotational impacts upon the anvil; and alubricant-impregnated bushing disposed within the front casing, thebushing rotatably supporting the anvil.
 12. The impact tool of claim 11,wherein the bushing gradually releases lubricant over time.
 13. Theimpact tool of claim 11, wherein the bushing is insert-molded within thefront casing.
 14. The impact tool of claim 11, wherein the driveassembly further includes a gear assembly coupled between the electricmotor and the shaft, wherein the gear assembly is at least partiallyhoused within the front casing.
 15. The impact tool of claim 11, whereinthe bushing has an impregnation ratio between about 5% and about 25%.16. The impact tool of claim 15, wherein the bushing has an impregnationratio between about 10% and about 20%.
 17. A method of manufacturing apower tool, the method comprising: forming a bushing from powdered metalby compacting and sintering the powdered metal; inserting the bushinginto a mold cavity; molding a gear case of the power tool in the moldcavity around the bushing; and immersing the gear case in lubricant suchthat the lubricant is wicked into the bushing to impregnate the bushingwith the lubricant.
 18. The method of claim 17, wherein the lubricant isan oil.
 19. The method of claim 17, wherein the bushing absorbs thelubricant to an impregnation ratio between about 5% and about 25%. 20.The method of claim 19, wherein the bushing absorbs the lubricant to animpregnation ratio between about 10% and about 20%.
 21. The method ofclaim 17, further comprising machining the gear case prior to immersingthe gear case in lubricant.
 22. The method of claim 17, furthercomprising inserting an anvil of the power tool into the bushing suchthat the bushing rotatably supports the anvil in the gear case.
 23. Themethod of claim 17, further comprising ultrasonically cleaning the gearcase prior to immersing the gear case in lubricant.